1. Blot dry ribs with paper towels. Sprinkle ribs with 1/4 teaspoon each salt and black pepper. Heat oil in a large nonstick skillet over medium-high heat. Cook meat for 5 minutes, turning once halfway through, in batches if necessary. Remove meat to slow cooker.
2. Add onion to skillet and cook, 2 minutes, stirring often. Add broth, 1 cup of the beer, the sugar and thyme to skillet. Bring to a boil, then pour over meat. Cover and cook on HIGH for 5 hours or LOW for 7 hours.
3. When there is 1 1/2 hours cook time remaining on HIGH or 2 1/2 hours on LOW, stir carrots and mushrooms into slow cooker.
4. Whisk together remaining 1/4 cup beer, 1/4 teaspoon each salt and pepper, and the cornstarch and mustard. Whisk into slow cooker. Replace cover and cook 15 more minutes or until sauce has thickened. Serve over egg noodles, if desired. Makes 8 servings.